This disclosure is related to protection of electrical receptacles, more particularly, to tamper resistance, arc fault protection, ground fault protection, overcurrent protection, and surge suppression for electrical receptacles and similar devices.
Conventional tamper resistive (TR) electrical receptacles employ mechanical means such as spring loaded gates, shutters or sliders on each of the outlet sockets to prevent insertion into the outlets of objects other than prongs of electrical plugs. Shutters or gates on each outlet socket must be pushed simultaneously to allow prong entry. Preclusion of foreign objects serves to avoid the likelihood of shock, burn or electrocution.
Conventional TR devices, however, have inherent disadvantages. Excessive force may be required to open the gates, as the plug blades must be perpendicular to the front face of the outlet and well aligned prior to simultaneous opening of the shutters. Often an equivalent force must be exerted on each blade in order to open the gates. These receptacles are thus difficult to use when located close to the floor or behind an article of furniture, especially for elderly and special needs individuals. Once the blades pass a tamper resistance gate and make contact with the sprung outlet terminals, the blades attain power even though they may not be completely inserted. Until the blades are fully removed past the tamper resistant gates or shutters the blades remain energized. Exposed blades prior to complete insertion or removal can result in arcing and electric shock. Moreover, with a live load connected with the TR receptacle, an arc fault circuit interrupter (AFCI) may false trip.
Various conventional circuit interruption devices exist for arc fault protection, ground fault protection, overcurrent protection, and surge suppression. An arc fault is an unintentional electrical discharge in household wiring characterized by low and erratic voltage/current conditions that may ignite combustible materials. A parallel current fault results from direct contact of two wires of opposite polarity. A ground current fault occurs when there is an arc between a wire and ground. A series voltage fault occurs when there is an arc across a break in a single conductor. When a ground or arc fault is detected, power is conventionally terminated on the circuit by an AFCI or ground fault circuit interrupter (GFCI) disconnecting both receptacle outlets and any downstream receptacles.
The devices include transformers that combine magnetic representations of the current in an analog form. Transformer current sensors are limited to a fixed current value and time interval. Upon sensed voltage imbalance of greater than a specified level, such as 6 mV, power is interrupted by electromechanical means, such as solenoid tripping a locking mechanism. The conventional devices lack capability to disconnect outlets individually, independently of other loads connected to the outlet.
A normal arc can occur when a motor starts or a switch is tripped. Only current flow imbalance between the hot and neutral conductors is detected by conventional circuit interrupters. The individual current line difference is not monitored. Conventional circuit interrupters trip frequently by false triggers, as they lack adequate capability to distinguish between normal arcing and unwanted arcing. Transformer current sensors are limited to a fixed current value and time interval. Upon sensed voltage imbalance of greater than a specified level, such as 6 mV, power is interrupted by electromechanical means, such as solenoid tripping a locking mechanism. The conventional devices lack capability to disconnect outlets individually, independently of other loads connected to the outlet.
As indicated above, needs exist to improve the usability and safety of existing conventional receptacles. Existing conventional GFCI and AFCI receptacles do not provide detail about a fault. Currents are not being individually measured. Existing conventional GFCI and AFCI receptacles do not measure, monitor and control current and voltage, and do not protect against overcurrent, under voltage or over voltage at the outlet. It would be desirable to limit interruption of power to affected outlets, receptacles or devices only on the circuit, based on the type and location of the fault. Overcurrent protection at the outlet is preferable to the protection provided by the circuit breaker as it would avoid delay as well as associated voltage losses associated with wire resistance along increasing wire length. Such voltage losses impede the ability of existing circuit breakers to detect a short circuit at a remote location.
There is a need for overcurrent protection that more effectively distinguishes between short circuits, momentary overcurrent and overload so that false triggering can be avoided. There is a need for a receptacle that can provide local overcurrent protection as well as protection against arc faults and ground faults.
Conventional existing dual amperage receptacles will supply up to 20 A to an appliance rated for 15 A and potentially cause an overcurrent event. There is a need for a dual amperage (e.g. 15 A/20 A) receptacle that restricts amperage supplied to a lower rated plug when a low rated appliance is plugged in.
Current measurement accuracy is important for effective ground and arc fault detection as well as overcurrent protection. Conventional receptacles are factory calibrated and not re-calibrated by the device once installed. There is a need for continued self-calibration of receptacles and outlets.
If the hot and neutral conductors have been incorrectly wired to the receptacle terminals, electrical equipment plugged into the receptacle can be damaged. Incorrect wiring can cause short circuits with potential to harm the user through shock or fire. There is a need to warn the receptacle installer that the receptacle has been incorrectly wired and to preclude supply power to the load in such event. It would also be desirable that the outlet not be operational if the black wire and white wire are incorrectly connected to the opposite terminals.
Conventional outlets lack surge protection features, which are typically provided by power strips and power bars. A power strip is inserted into a receptacle after which a sensitive electrical device is plugged into one of the power strip extension receptacles. Use of the power strip tends to lead to a false impression that it is safe to insert additional loads that more than permissible. There is a need for surge protection at the electrical receptacle to avoid use of a dedicated power strip and its attendant disadvantages of power loss and limited life.
It is possible to plug a GFI extension cord or a power strip with a comprised ground prong into a two blade ungrounded receptacle by using a “cheater plug” that allows the ground prong to be inserted without a present ground. It is also possible to replace an ungrounded two blade electrical receptacle with one with ground socket without actually providing a conductor to ground pin. Conventional existing receptacles do not indicate that the supply side safety ground is present or if it is compromised. There is a need to protect the user and the equipment in the event of an incorrect grounding of an electrical receptacle. If no safety-ground is present and a wire conductor is exposed (e.g. has degraded insulation) the user may act as the ground path and receive a shock.
Traditionally, GFCI manual testing is accomplished by injecting a current imbalance. A thoroid type transformer is typically used to measure the current imbalance between neutral and hot conductors. The monitoring circuit indicates that an imbalance has occurred without indicating the amount of imbalance. This method is limited in that the absolute value of current imbalance is not available. There is merely a voltage level that indicates that an imbalance or fault has occurred. There is a need for more comprehensive self-testing and interruption of supply power to downstream and/or receptacle loads upon fault detection or an internal component fault.